Fire-resistant safes are designed to protect their contents from exposure to high temperatures of fire for predetermined periods of time. The safes are usually constructed with external and internal shells that encapsulate a space filled with insulating material. The external shell forms the outer surface of the safe and cooperates with the internal shell to form a shuttering for molding the insulation material in place within walls of the safe. The insulation material is generally made of a mixture that solidifies in a mold but retains a large amount of water within the solidified mass of the material.
Fire-resistant safes also have openings for receiving contents; and the openings in safe bodies are closed by doors, drawer heads, or other types of closures for protecting the contents of the safes. The closures may also be constructed with external and internal shells filled with the same insulating material. The openings in the safe bodies are surrounded by a frame that joins the external and internal shells of the safe bodies. Similarly, the external and internal shells of the closures are joined by a peripheral region that fits within the frame of the safe bodies to close the openings in the safes.
The external and internal shells of many fire-resistant safes are made of steel to provide additional structural strength and to conduct heat away from hot spots by dissipating the heat over a larger area of the safes. However, intermediate portions of the steel shells, which form the frames in the safe bodies and the peripheral regions of the closures, conduct heat into the interior of the safes. In addition, the steel shells tend to warp when heated and produce, between the safe openings and the closures, passages that admit hot gasses into the safes.
Other fire-resistant safes have external and internal shells made of a molded resin material. Although the resin material is combustible and burns away from the outer surfaces of the insulation material in a fire, the resin material of the frames and the peripheral regions of the closures only partially melts away leaving a seal between the safe openings and closures. The frames of the safe openings and closures are made deep enough in cross section through the safes so that, after the resin material covering the outer surfaces of the insulation material has burned away, a softened or plasticized portion of the resin material remains in the opening to seal the closures to the safe bodies. The resin seal resists heat conduction and the passage of hot gasses into the safes.
However, since the resin material of the shells exhibits low thermal conductivity in relation to steel, the resin shells do not dissipate as much heat away from hot spots. The corners of the safes are especially vulnerable to "burn through" because the corners are exposed to heat on three sides. Accordingly, additional insulating material is used in the corners of the safes to provide more uniform protection against burn through over the exposed areas of the safes.
In addition to the heat concentrations in portions of the safes exposed to fire from more than one direction, other heat concentrations are evident in front walls of the safes at the top corners of the frames joining jamb members that enclose opposite sides of the openings with a framing member that encloses the top of the openings. Under especially severe conditions, the resin material in the top corners of the frames may be entirely burned away exposing a hole through the resin seal between the safe openings and closures.